1. Field of the Invention
The present invention relates to a binding for binding a boot to a gliding board. The invention relates in particular to the rear portion of a binding for binding a boot on a gliding board, such binding referred to as the heel-piece. The invention includes a particularly advantageous application of a binding for alpine ski boot bindings and, in particular, for the so-called ski touring bindings.
2. Background Description
In the descent, or descent phase, a solution for fixing a boot to a gliding board, such as a ski, involves using a front portion of the binding, referred to as the toe-piece, designed to affix the front of the boot to the board, and a heel-piece to fix the heel of the boot to the board.
According to an embodiment disclosed in the document AT 402 020, the heel-piece supports two rods each having a free end which is adapted to penetrate into a respective corresponding housing formed in the heel of the boot as disclosed, for example, in the document EP 0 199 098.
When the heel of the boot is to be fixed to the board, it suffices to bring the heel downward, which results in a collaboration between the two rods and the heel. The two rods then engage in the housing of the heel and block it. The heel is then affixed to the board and thus ensures proper retention of the foot when gliding.
In certain situations, for example in the event of a fall of the user, the boot must be capable of being released immediately from the binding. For this purpose, the binding incorporates one or more mechanisms that enable automatic release of the boot in the area of the heel-piece and/or in the area of the toe-piece. This function is called a “release”.
Thus, in certain constructions, such as those disclosed in the documents WO 2012/024809, US 2013/0181427, WO 2009/105866, EP 2 570 160, and U.S. Pat. No. 8,820,772, the release can be performed essentially by the heel-piece. This release occurs as a result of a substantial force directed:                either vertically, that is to say, the heel is lifted from the gliding board along a direction substantially perpendicular to the upper surface of the gliding board. This release is called a “vertical release” and occurs after a forward fall of the skier;        or laterally, that is to say, the heel is disengaged from the gliding board along a circular arc, the vertical axis of rotation of which is substantially at the front of the boot. In general, the release is generated by a torque exerted on the boot about this vertical axis of rotation. This torque can be transposed by a force along a direction substantially transverse to the gliding board, i.e., substantially perpendicular to the longitudinal direction of the gliding board. This release is called a “lateral release”. During lateral release, the body of the heel-piece which supports the rods is rotationally driven about an axis perpendicular to the upper surface of the gliding board.        
The general principle of blocking the heel-piece, as well as the mechanisms enabling the automatic vertical and lateral releases in the event of fall are described below.
The heel-piece generally comprises a plurality of holding mechanisms, typically springs, which exert a force tending to move the two free ends of rods closer to one another or to return them to a neutral position. The distance between the two free ends of the rods is thus constrained elastically.
Typically, as illustrated in the documents EP 2 420 306, US 2012/0042542, and EP 0 199 098, the boot heel housing defines two guiding paths symmetrical in relation to a median axis of the foot. Each of the two guiding paths has an engagement zone in which a rod of the heel-piece is adapted to penetrate when the heel gets close to the heel-piece. Each of the two guiding paths is then extended by a guiding zone in which one of the rods is guided until reaching a blocking zone. In this configuration, the heel is held firmly in the heel-piece, both vertically and laterally. During insertion of the heel of the boot in the heel-piece, the two guiding zones, each associated with a rod, mutually space apart the two ends of the rods, which come closer together upon reaching the blocking zone. From the blocking zone, the springs of the heel-piece tend to bring the two free ends of the rods closer together and to hold them in the blocking zone.
To separate the heel from the heel-piece, the free ends of the rods of the heel-piece must move away from the associated blocking zones.
For a vertical release, it is necessary to overcome the force generated by the holding mechanisms in order to space the two free ends of the rods sufficiently apart and to extract them from the blocking zone until bringing them on the guiding zone.
For a lateral release, it is necessary to turn the heel-piece in order to move the free ends of the rods away from the blocking zones. In this case, the ends exit directly from the associated blocking zones, without passing through the guiding zones.
Certain known solutions disclosed in the previously mentioned documents provide relatively complex devices with:                first mechanisms, usually first springs, acting on the rods to maintain a predetermined spacing of the ends thereof. When a vertical force exerted by the foot is greater than a vertical release threshold, the heel, i.e., the guiding paths, acts on the rods so as to cause a spacing of the ends of the rods that is sufficient to tilt them into the guiding zone, thereby releasing the boot from the heel-piece. If the vertical force is less than the vertical release threshold, the ends remain engaged in the blocking zones,        second release mechanisms, usually second springs, different from the first springs, acting on the body of the heel-piece to maintain it in a predetermined angular position. When a torque about a vertical axis is exerted on the boot, this translates into a lateral force exerted by the foot on the heel-piece. The heel then acts on the rods so as to cause rotation of the body of the heel-piece about a vertical axis, against the force exerted by the first release mechanisms. As soon as the body reaches a specific angle, the rods disengage from the blocking zone 12, and the boot is released from the heel-piece. This angle is reached as soon as the lateral force is greater than a lateral release threshold. If the force is less than this threshold, the rods remain engaged in the blocking zones 12.        
These solutions are complex. Furthermore, they are relatively heavy. However, lightness is critical to the performance of a binding. This is especially true in the case of ski touring, in which the user must lift his skis during an ascent.
The document EP 2 384 794 proposes a solution in which two springs urge the two rods for the vertical release. Furthermore, the same springs are part of the lateral release mechanism.
In this document, the main body supporting the rods is rotationally driven around a base during lateral release. The main body also supports a control body provided with a pin, extending vertically downward. The control body is constrained by springs housed in the main body. The pin cooperates with a V-shaped cam surface formed on the base. During lateral release, the body turns. The pin then engages the cam surface of the base, thereby causing a sliding displacement of the control body tending to constrain the springs. Thus, in order to turn the body, sufficient lateral force must be exerted to enable compression of the springs. The cam surface and the dimensioning of the springs define the lateral force to be exerted to obtain a predetermined rotation angle of the body. During lateral release, all of the force is transferred from the cam surface to the pin, thus making the system relatively fragile. During lateral release, only a single rod is biased to rotate the body. The lateral release is defined only by the cam surface of the base and the springs, independently of the rods and more particularly of their spacing. The rods are not biased into moving apart. Furthermore, the mechanism has a height space requirement because the vertical release mechanism and the lateral release mechanism are superposed vertically. Although the device has a reduced number of components as compared with similar heel-pieces, it still comprises a large number of components. In addition, the kinematics of the control body has a plurality of contact and friction zones which can interfere with proper operation of the release mechanisms through wear or jamming. The release values may then be corrupted.
However, winter sports, especially those practiced in the backcountry require very reliable equipment.